Oncolytic virotherapy relies on the induction of anti-
tumor immune responses to achieve therapeutic efficacy. The factors that influence the induction of these responses, however, are not well understood. To begin to address this lack of knowledge, we asked how decreasing the susceptibility of malignant cells to direct
viral infection would impact the induction of immune responses and therapeutic efficacy caused by oncolytic myxoma virus treatment. To accomplish this, we used CRISPR-Cas9 genome editing to remove the essential sulfation
enzyme N-deacetylase/N-
sulfotransferase-1 from B16/F10 murine
melanoma cells. This eliminates the negative cell surface charges associated with
glycosaminoglycan sulfation, which reduces a cell's susceptibility to
infection with the myxoma virus by ∼3- to 10-fold. With the use of these cells as a model of reduced susceptibility to oncolytic
infection, our data demonstrate that 3- to 10-fold reductions in in vivo
infection do not hinder the ability of the oncolytic myxoma virus to induce anti-
tumor immunity and do not lower the overall efficacy of localized treatment. Additionally, our data show that in mice bearing multiple distinct
tumor masses, the choice to treat a less-susceptible
tumor mass does not reduce the overall therapeutic impact against either the injected or noninjected lesion. Taken together, these data suggest that minor changes in the susceptibility of malignant cells to direct oncolytic
infection do not necessarily influence the overall outcomes of treatment.